You should totally open-source that, put it on NPM, and write an article or so about it.
Everyone will have different set of methods they use. Point of this is that if you need some method you can just add it in in 4-5 lines or remove one you don't need. So it's not the best fit for NPM. It's good fit for good old copy/paste into a project, if you're optimizing for size/memory use. :)
https://megous.com/dl/tmp/basic.js
1.3kB compressed. Much better. :) And I avoided having to rewrite my extensions with platform APIs. That was before FF killed all the joy in writing userscripts for me, because I was no longer able to install and update them just by copying them to mozilla folder and had to invoke a lot of clicking ceremony to just get my 20 scripts or so from git into firefox past the webextension limitations on storage/access to mozilla folder.